In desktop computing, it is now common to use more than one display device such as an external monitor or even a projector (“Display”). Traditionally, a user would have a computer with a single Display attached, but now it is possible to have more than one Display attached to the computer, which increases the usable area for the worker. For example, International Patent Application Publication WO 20071020408 discloses a display system comprising a plurality of Displays, each displaying respectively an image; a data processing device connected to each Display and controlling the image displayed by each Display; and a user interface device connected to the data processing device. Connecting multiple Displays to a computer is a proven method for improving productivity.
The connection of an additional Display to a computer presents a number of problems. In general, a computer will be provided with only one video output such as a VGA-out connection. One method by which a Display can be added to a computer is by adding an additional graphics card to the internal components of the computer. The additional graphics card will provide an additional video output which will allow another Display to be connected to the computer and driven by that computer. However, this solution is relatively expensive and is not suitable for many non-technical users of computers.
An alternative method of connecting a Display is to connect the Display to a USB or other general purpose data protocol socket on the computer (“Host”) that generates the display data, as all modern computers are provided with multiple USB sockets. This provides a simple connection topology, but requires additional hardware and software (a “Display Control Device”) to be present, as in general, USB has a bandwidth that makes the provision of a good quality video output a non-trivial task.
As display technologies improve and the user's desire for display quality increases, the requirements placed upon the Display Control Device that is receiving the incoming display data will correspondingly increase as the amount of display data will increase proportionally. For this reason, combined with limited bandwidth available, for example in a USB connection, it is often necessary to send display data in compressed form. However, compressed data often contains artefacts that become visible on the display device where some data has been lost due to the compression process. Consequently, if there is a reduction in the amount of data being transmitted, for example because the display image is static, it may be beneficial to send uncompressed data—known as ‘raw’ data—to ‘heal’ the problematic area of the displayed image.
Some known display systems make use of spatially independent groups of one or more pixels (known as “tiles”). A tile may comprise a single pixel, or may comprise a tile of 2×2, 4×4 or any other appropriate number of pixels. Furthermore, a tile may be rectangular, rather than square in shape. Tiles may be sent as compressed data or as raw data. However, in presently known systems display data of one type must be sent for the whole of a particular frame of the display and the system must reconfigure in order to be able to deal with display data of the other type for another frame.
The present invention aims to reduce or mitigate this problem.